The two Johns stuffed up their surface protocols. John Wright did the core SP fine but then dipped his airways below the surface while looking for his tag within the 30 sec (I think) that he needed to keep them clear and John P did a clean 60m FIM dive but thought he was still in training mode and "pretended" to remove his mask rather than actually doing it! No doubt he is frustrated. Phil C leads at the end of day one with a clean 50m no-fins dive.

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How much does the water temp affect (if at all) the depths that these guys are going for?

That's classic that John P ran foul of thinking he was still in training with a mask removal simulation. Relying on training when stress levels are high or cognitive function is low is fine unless the skills you are reinforcing are incomplete or ineffective. There are some quite sobering examples of this sort of thing happening with far greater consequences than just disqualification.

Water temp does have an impact - as does visibility. Hitting a deep thermocline as you sink can cause you to lose (i.e. swallow) your mouthfill (for equalising). Apparently there is often a deepish thermocline in Lake Taupo at somewhere between 20m and 30m and this has upset a few good divers in the past.

Yes, it is common practice to simulate mask removal when training - this is so we don't pepper the bottom of the lake with a lot of masks (otherwise I know a good spot in 45m of water in Lake Pupuke that would be a fertile collecting ground for masks).

And the temperature also means divers will be wearing thicker wetsuits which means greater buoyancy change as you dive - making certain parts of a dive harder e.g. leaving the surface for the first part of the dive down to the point where you become negatively buoyant and then when you start the swim back up from the bottom plate.